Conventionally, a laminated core for a stepping motor has a very small air gap between a rotor and a stator. When a rotor core sheet and a stator core sheet, respectively used for the rotor and the stator, are produced from one thin strip material, small metal clippings are formed in narrow gaps therebetween. The metal clippings may be broken during a punching operation and not drop into a downside of a die, a part of a die device, thereby requiring the punching operation again. What is worse, the die device may be damaged due to clogging of scraps including the metal clippings.
If magnetic pole pieces, specifically magnetic pole teeth located radially inside the stator core sheet, cannot be blanked in a desired shape, the rotor core sheet and the stator core sheet have to be blanked using the different die devices, which results in a low material yield and a high cost.
Patent Literature 1 discloses an example of the conventional art to solve the above problems. In Patent Literature 1, at least one of the rotor core sheet and the stator core sheet are coined, specifically, pressed in a thickness direction and evenly elongated so as to form thin sections. Further, both of the rotor core sheet and the stator core sheet can be produced from one magnetic steel sheet using one die device.
In a method for manufacturing a laminated core of Patent Literature 1, the thin section is elongated in a circumferential direction, and bulges are formed in an area where a wire is wound. As a countermeasure, Patent Literature 2 discloses a finishing blanking for eliminating the bulges on lateral sides of the magnetic pole teeth.